The present invention relates to polyurethane foams having a closed cell content of at least 90% and improved heat sag properties produced by reaction injection molding (xe2x80x9cRIMxe2x80x9d) and to a process for the production of such foams.
RIM processes for the production of polyurethane foams are well known. See, for example, Oertel, Polyurethane Handbook, 2d Ed., (copyright)1994, Section 7.4, pages 368-385 and U.S. Pat. Nos. 5,026,739; 5,225,453; 5,837,172; and 6,005,016.
In these known processes, an organic diisocyanate or polyisocyanate is reacted with an isocyanate-reactive component that includes at least one (generally more than one) polyol, a catalyst, a cross-linking agent and other processing aids. The polyols used are those which are typically derived from sources such as sucrose, amines, glycerine, ethylene glycol, etc. Many of these starting materials are derived from increasingly expensive petrochemicals. It would therefore be advantageous to substitute some or all of these polyols with polyols derived from less expensive starting materials.
Alternative sources for such polyols which have been proposed are renewable sources such as vegetable oils (e.g., soybean oil, castor oil, linseed oil, tung oil, peanut oil, sunflower oil) and fish oils.
U.S. Pat. No. 2,787,601, for example, discloses cellular, flexible polyurethanes made with hydroxyl-group containing fatty acid glycerides. More specifically, a simple (i.e., unmodified) and untreated hydroxyl-group containing fatty acid glyceride such as castor oil is reacted with an aromatic diisocyanate to form an isocyanate-terminated prepolymer. This prepolymer is then reacted with water to form a cellular foam having reported apparent densities of from 2.8 to 6.5 pounds per cubic foot.
U.S. Pat. No. 2,833,730 also discloses cellular polyurethanes produced from a polyol based on a fatty acid triglyceride which reportedly do not have the shrinkage problems encountered with similar, prior art polyurethanes made from such polyols. More specifically, a mixture of a low molecular weight polyhydroxyl compound and a hydroxyl group-containing triglyceride (unmodified and untreated) is reacted with an aromatic diisocyanate to form an isocyanate-terminated prepolymer. This prepolymer is then reacted with water to form the desired polyurethane product. The ratio of the low molecular weight polyhydroxyl compound to the hydroxyl-group containing triglyceride should be at least 0.6 to 1 in order to obtain a polyurethane having the improved shrinkage property.
Unmodified vegetable oils have not, however, been used as a major reaction component to produce rigid polyurethane foams by a RIM process.
Use of unmodified vegetable oils as a major substituent of a polyol component used to produce rigid polyurethane foams is, however, disadvantageous because the unmodified vegetable oil tends to migrate to the polyurethane surface over time and thereby increase the potential for problems after a molded part is painted and reduction of physical properties.
In an effort to improve the physical properties of foams produced from vegetable oils, those vegetable oils have been chemically modified prior to use. U.S. Pat. No. 4,742,087, for example, discloses a process in which the epoxidized oils are partially converted by alcoholysis or transesterification to alkyl ester polyols which are used to produce isocyanate-terminated prepolymers. These prepolymers are subsequently reacted to produce polyurethane foams.
U.S. Pat. No. 5,482,980 discloses a process for the production of flexible open-celled, urethane foams in which epoxidized soybean oil is included in the polyether polyol reaction component.
Epoxidized vegetable oils have also been used in relatively minor amounts in polyurethane-forming reaction mixtures as emulsifiers. See, e.g., U.S. Pat. No. 5,750,583.
Such chemically modified oils have not, however, been used as a significant portion of the polyol component used to produce rigid, closed-cell polyurethane foams because at higher levels these types of materials would be expected to function in the same manner as internal mold release agents and increase the potential for de-lamination when molding composite articles.
The use of modified vegetable oils is also commercially disadvantageous due to the energy, materials and time required for epoxidation and any subsequent conversion, e.g., to a polyester polyol.
One alternative to such chemically modified vegetable oils is disclosed in U.S. Pat. No. 6,180,686. In this patent, urethane foams and elastomers are produced by reacting an isocyanate with a vegetable oil which has been treated by passing air through the oil to remove impurities and thicken the oil (referred to as xe2x80x9cblown oilxe2x80x9d) in the presence of a multi-functional alcohol crosslinking agent such as butanediol or ethylene glycol. The blown oil is used as the sole isocyanate-reactive component. No petroleum-based polyester or polyether polyol is included. Rigid, closed-celled polyurethane foams are not, however, taught to be producible with the disclosed blown vegetable oils.
It would therefore be advantageous to develop a process in which rigid, closed cell, polyurethane foams may be produced by a RIM process using as a polyol component an unmodified renewable source such as a vegetable oil without sacrificing the physical properties of that rigid foam.
It is an object of the present invention to provide a polyol component useful in the production of rigid, closed-cell polyurethane foams which polyol component includes a bio-based polyol material as a significant component.
It is also an object of the present invention to provide a RIM process for the production of rigid, closed-cell polyurethane foams having good physical properties from a reaction mixture which includes a significant amount of a bio-based polyol material.
These and other objects which will be apparent to those skilled in the art are accomplished by including up to 30% by weight, based on total weight of isocyanate-reactive component, of a blown bio-based oil (also referred to herein as a xe2x80x9cbio-based polyolxe2x80x9d or xe2x80x9cblown vegetable oilxe2x80x9d or a xe2x80x9cpolymerized vegetable oilxe2x80x9d) such as soybean oil in an isocyanate-reactive component to be used in a RIM process.